The present invention relates to a method of treating grinding wheels, and more particularly to improvements in a method of dressing and thereupon finishing (sharpening) the working surfaces of grinding wheels, especially grinding wheels which contain cubic boron nitride.
A grinding wheel which contains cubic boron nitride is normally treated first by a dressing tool and thereupon by a pressure applicator simultaneously with admission of hard pulverulent finishing or sharpening material into a gap which is established between the pressure applicator and the working surface of the grinding wheel. The pressure applicator can constitute a workpiece which has been ground in a grinding machine, a specially designed shoe which is capable of defining with the working surface of the grinding wheel a gap of requisite width, or a roll which is mounted in the frame of the grinding machine and can be moved to a requisite position with reference to the working surface of the grinding wheel upon completion of the dressing operation. The particulate material which is used in conjunction with the pressure applicator to finish the working surface of the grinding wheel can be admitted in a suitable carrier medium such as wax, lubricating grease, liquid coolant or even air. As a rule, the finishing operation is regulated in that the force with which the pressure applicator bears against the particles of finishing material in the aforementioned gap is varied in the course of the finishing or sharpening operation. Reference may be had to U.S. Pat. No. 3,314,410 granted Apr. 18, 1967 to Knauer et al. as well as to the article "High-speed dressing of BORAZON CBN wheels" by Philipp E. Bonnice in "Cutting Tool Engineering", January/February 1975. It is further known to select the width of the gap between the working surface of the grinding wheel and the adjacent surface of the pressure applicator in dependency on the diameters of particles which are used in the course of the finishing operation. Reference may be had to German Auslegeschrift No. 10 80 433 and to German Offenlegungsschrift No. 26 39 058.
In order to ensure the establishment of a gap of requisite width (namely a gap which ensures that the particles are properly urged against the working surface of the grinding wheel so as to complete the finishing operation with little loss in time and to simultaneously place such working surface in optimum condition for the ensuing treatment of workpieces) as a function of the dimensions of particles which are used to carry out the finishing operation, it was already proposed to grind the pressure applicator (e.g., a rotary disc-shaped member) upon completion of each finishing operation. The extent of grinding of the pressure applicator was selected with a view to correspond to more pronounced wear upon the dressing tool in order to compensate for a change in the width of the gap as a result of more pronounced wear upon the dressing tool (than upon the pressure applicator) and for the ensuing change in the positions of wheel-engaging surfaces of the dressing tool and pressure applicator relative to each other (reference may be had to the aforementioned German Offenlegungsschrift No. 26 39 058). Such proposal failed to gain acceptance in the relevant industries and was not developed further because its reliability and utility are predicated on the assumption that the wear upon the dressing tool in the course of a dressing operation is more pronounced than the wear upon the pressure applicator in the course of a finishing or sharpening operation. Such situation is highly unlikely to arise, or it arises only infrequently under exceptional circumstances, because the dressing tool normally carries diamonds so that the wear upon such tool is minimal or non-existent. At any rate, the wear upon a dressing tool whose wheel-contacting surface is studded with industrial diamonds is incomparably less pronounced than that upon a pressure applicator. In fact, in many or in most instances, the wear upon the dressing tool (in contrast to the wear upon the pressure applicator) is so minimal that it can be disregarded in its entirety.